3D semiconductor device and structure

ABSTRACT

A 3D semiconductor device, the device including: a first level including a single crystal layer, a first metal layer, a second metal layer above the first metal layer, and a third metal layer above the second metal layer, where the second metal layer is significantly thicker than either the third metal layer or the first metal layer, where the third metal layer is precisely aligned to the first metal layer with less than 20 nm misalignment; a second level including a first array of first memory cells, each of the first memory cells include first transistors; a third level including a second array of second memory cells, each of the second memory cells include second transistors, where the second level is above the third level, where the second transistors are self-aligned to the first transistors, being processed following the same lithography step; and periphery circuits connected by the second metal to control the memory cells, where the periphery circuits are either underneath or atop the memory cells.

CROSS-REFERENCE OF RELATED APPLICATION

This application is a continuation in part of U.S. patent application Ser. No. 17/114,155, which was filed on Dec. 7, 2020, which is a continuation in part of U.S. patent application Ser. No. 17/013,823, which was filed on Sep. 7, 2020, which is a continuation in part of U.S. patent application Ser. No. 16/409,813, which was filed on May 11, 2019, and now is U.S. Pat. No. 10,825,864 issued on Nov. 3, 2020, which is a continuation in part of U.S. patent application Ser. No. 15/803,732, which was filed on Nov. 3, 2017, and now is U.S. Pat. No. 10,290,682 issued on May 14, 2019, which is a continuation in part of U.S. patent application Ser. No. 14/555,494, which was filed on Nov. 26, 2014, and now is U.S. Pat. No. 9,818,800 issued on Nov. 14, 2017, which is a continuation of U.S. patent application Ser. No. 13/246,157, which was filed on Sep. 27, 2011 and now is U.S. Pat. No. 8,956,959 issued on Feb. 17, 2015, which is a continuation of U.S. patent application Ser. No. 13/173,999, which was filed on Jun. 30, 2011 and now is U.S. Pat. No. 8,203,148 issued on Jun. 19, 2012, which is a continuation of U.S. patent application Ser. No. 12/901,890, which was filed on Oct. 11, 2010, and now is U.S. Pat. No. 8,026,521 issued on Sep. 27, 2011.

BACKGROUND OF THE INVENTION 1. Field of the Invention

This invention describes applications of monolithic 3D integration to at least semiconductor chips performing logic and memory functions.

2. Discussion of Background Art

Over the past 40 years, one has seen a dramatic increase in functionality and performance of Integrated Circuits (ICs). This has largely been due to the phenomenon of “scaling” i.e. component sizes within ICs have been reduced (“scaled”) with every successive generation of technology. There are two main classes of components in Complimentary Metal Oxide Semiconductor (CMOS) ICs, namely transistors and wires. With “scaling”, transistor performance and density typically improve and this has contributed to the previously-mentioned increases in IC performance and functionality. However, wires (interconnects) that connect together transistors degrade in performance with “scaling”. The situation today is that wires dominate performance, functionality and power consumption of ICs.

3D stacking of semiconductor chips is one avenue to tackle issues with wires. By arranging transistors in 3 dimensions instead of 2 dimensions (as was the case in the 1990s), one can place transistors in ICs closer to each other. This reduces wire lengths and keeps wiring delay low. However, there are many barriers to practical implementation of 3D stacked chips. These include:

-   -   Constructing transistors in ICs typically require high         temperatures (higher than −700° C.) while wiring levels are         constructed at low temperatures (lower than −400° C.). Copper or         Aluminum wiring levels, in fact, can get damaged when exposed to         temperatures higher than −400° C. If one would like to arrange         transistors in 3 dimensions along with wires, it has the         challenge described below. For example, let us consider a 2         layer stack of transistors and wires i.e. Bottom Transistor         Layer, above it Bottom Wiring Layer, above it Top Transistor         Layer and above it Top Wiring Layer. When the Top Transistor         Layer is constructed using Temperatures higher than 700° C., it         can damage the Bottom Wiring Layer.     -   Due to the above mentioned problem with forming transistor         layers above wiring layers at temperatures lower than 400° C.,         the semiconductor industry has largely explored alternative         architectures for 3D stacking. In these alternative         architectures, Bottom Transistor Layers, Bottom Wiring Layers         and Contacts to the Top Layer are constructed on one silicon         wafer. Top Transistor Layers, Top Wiring Layers and Contacts to         the Bottom Layer are constructed on another silicon wafer. These         two wafers are bonded to each other and contacts are aligned,         bonded and connected to each other as well. Unfortunately, the         size of Contacts to the other Layer is large and the number of         these Contacts is small. In fact, prototypes of 3D stacked chips         today utilize as few as 10,000 connections between two layers,         compared to billions of connections within a layer. This low         connectivity between layers is because of two reasons: (i)         Landing pad size needs to be relatively large due to alignment         issues during wafer bonding. These could be due to many reasons,         including bowing of wafers to be bonded to each other, thermal         expansion differences between the two wafers, and lithographic         or placement misalignment. This misalignment between two wafers         limits the minimum contact landing pad area for electrical         connection between two layers; (ii) The contact size needs to be         relatively large. Forming contacts to another stacked wafer         typically involves having a Through-Silicon Via (TSV) on a chip.         Etching deep holes in silicon with small lateral dimensions and         filling them with metal to form TSVs is not easy. This places a         restriction on lateral dimensions of TSVs, which in turn impacts         TSV density and contact density to another stacked layer.         Therefore, connectivity between two wafers is limited.

It is highly desirable to circumvent these issues and build 3D stacked semiconductor chips with a high-density of connections between layers. To achieve this goal, it is sufficient that one of three requirements must be met: (1) A technology to construct high-performance transistors with processing temperatures below ˜400° C.; (2) A technology where standard transistors are fabricated in a pattern, which allows for high density connectivity despite the misalignment between the two bonded wafers; and (3) A chip architecture where process temperature increase beyond 400° C. for the transistors in the top layer does not degrade the characteristics or reliability of the bottom transistors and wiring appreciably. This patent application describes approaches to address options (1), (2) and (3) in the detailed description section. In the rest of this section, background art that has previously tried to address options (1), (2) and (3) will be described.

There are many techniques to construct 3D stacked integrated circuits or chips including:

-   -   Through-silicon via (TSV) technology: Multiple layers of         transistors (with or without wiring levels) can be constructed         separately. Following this, they can be bonded to each other and         connected to each other with through-silicon vias (TSVs).     -   Monolithic 3D technology: With this approach, multiple layers of         transistors and wires can be monolithically constructed. Some         monolithic 3D and 3DIC approaches are described in U.S. Pat.         Nos. 8,273,610, 8,298,875, 8,362,482, 8,378,715, 8,379,458,         8,450,804, 8,557,632, 8,574,929, 8,581,349, 8,642,416,         8,669,778, 8,674,470, 8,687,399, 8,742,476, 8,803,206,         8,836,073, 8,902,663, 8,994,404, 9,023,688, 9,029,173,         9,030,858, 9,117,749, 9,142,553, 9,219,005, 9,385,058,         9,406,670, 9,460,978, 9,509,313, 9,640,531, 9,691,760,         9,711,407, 9,721,927, 9,799,761, 9,871,034, 9,953,870,         9,953,994, 10,014,292, 10,014,318; and pending U.S. Patent         Application Publications and applications, Ser. Nos. 14/642,724,         15/150,395, 15/173,686, 62/651,722; 62/681,249, 62/713,345,         62/770,751, 62/952,222, 2020/0013791, 16/558,304; and PCT         Applications (and Publications): PCT/US2010/052093,         PCT/US2011/042071 (WO2012/015550), PCT/US2016/52726         (WO2017053329), PCT/US2017/052359 (WO2018/071143),         PCT/US2018/016759 (WO2018144957), and PCT/US2018/52332 (WO         2019/060798).     -   Electro-Optics: There is also work done for integrated         monolithic 3D including layers of different crystals, such as         U.S. Pat. Nos. 8,283,215, 8,163,581, 8,753,913, 8,823,122,         9,197,804, 9,419,031, 9,941,319, and 10,679,977.

U.S. Pat. No. 7,052,941 from Sang-Yun Lee (“S-Y Lee”) describes methods to construct vertical transistors above wiring layers at less than 400° C. In these single crystal Si transistors, current flow in the transistor's channel region is in the vertical direction. Unfortunately, however, almost all semiconductor devices in the market today (logic, DRAM, flash memory) utilize horizontal (or planar) transistors due to their many advantages, and it is difficult to convince the industry to move to vertical transistor technology.

A paper from IBM at the Intl. Electron Devices Meeting in 2005 describes a method to construct transistors for the top stacked layer of a 2 chip 3D stack on a separate wafer. This paper is “Enabling SOI-Based Assembly Technology for Three-Dimensional (3D) Integrated Circuits (ICs),” IEDM Tech. Digest, p. 363 (2005) by A. W. Topol, D. C. La Tulipe, L. Shi, et al. (“Topol”). A process flow is utilized to transfer this top transistor layer atop the bottom wiring and transistor layers at temperatures less than 400° C. Unfortunately, since transistors are fully formed prior to bonding, this scheme suffers from misalignment issues. While Topol describes techniques to reduce misalignment errors in the above paper, the techniques of Topol still suffer from misalignment errors that limit contact dimensions between two chips in the stack to >130 nm.

The textbook “Integrated Interconnect Technologies for 3D Nanoelectronic Systems” by Bakir and Meindl (“Bakir”) describes a 3D stacked DRAM concept with horizontal (i.e. planar) transistors. Silicon for stacked transistors is produced using selective epitaxy technology or laser recrystallization. Unfortunately, however, these technologies have higher defect density compared to standard single crystal silicon. This higher defect density degrades transistor performance.

In the NAND flash memory industry, several organizations have attempted to construct 3D stacked memory. These attempts predominantly use transistors constructed with poly-Si or selective epi technology as well as charge-trap concepts. References that describe these attempts to 3D stacked memory include “Integrated Interconnect Technologies for 3D Nanoelectronic Systems”, Artech House, 2009 by Bakir and Meindl (“Bakir”), “Bit Cost Scalable Technology with Punch and Plug Process for Ultra High Density Flash Memory”, Symp. VLSI Technology Tech. Dig. pp. 14-15, 2007 by H. Tanaka, M. Kido, K. Yahashi, et al. (“Tanaka”), “A Highly Scalable 8-Layer 3D Vertical-Gate (VG) TFT NAND Flash Using Junction-Free Buried Channel BE-SONOS Device,” Symposium on VLSI Technology, 2010 by W. Kim, S. Choi, et al. (“W. Kim”), “A Highly Scalable 8-Layer 3D Vertical-Gate (VG) TFT NAND Flash Using Junction-Free Buried Channel BE-SONOS Device,” Symposium on VLSI Technology, 2010 by Hang-Ting Lue, et al. (“Lue”) and “Sub-50 nm Dual-Gate Thin-Film Transistors for Monolithic 3-D Flash”, IEEE Trans. Elect. Dev., vol. 56, pp. 2703-2710, November 2009 by A. J. Walker (“Walker”). An architecture and technology that utilizes single crystal Silicon using epi growth is described in “A Stacked SONOS Technology, Up to 4 Levels and 6 nm Crystalline Nanowires, with Gate-All-Around or Independent Gates (ΦFlash), Suitable for Full 3D Integration”, International Electron Devices Meeting, 2009 by A. Hubert, et al (“Hubert”). However, the approach described by Hubert has some challenges including use of difficult-to-manufacture nanowire transistors, higher defect densities due to formation of Si and SiGe layers atop each other, high temperature processing for long times, difficult manufacturing, etc.

It is clear based on the background art mentioned above that invention of novel technologies for 3D stacked layer and chips will be useful.

SUMMARY

The invention may be directed to at least multilayer or Three Dimensional Integrated Circuit (3D IC) devices, structures, and fabrication methods.

In one aspect, a 3D semiconductor device, the device including: a first level including a first single crystal layer and first transistors, where the first transistors each include a single crystal channel; first metal layers interconnecting at least the first transistors; and a second level including a second single crystal layer and second transistors, where the second level overlays the first level, where the second transistors are horizontally oriented and each include at least two side gates, where the second level is bonded to the first level, and where the bonded includes oxide to oxide bonds.

In another aspect, a 3D semiconductor device, the device including: a first level including a first single crystal layer and alignment marks; first transistors overlaying the first single crystal layer; second transistors overlaying the first transistors; and a second level including a second single crystal layer, where the second level overlays the second transistors, where the first transistors and the second transistors are self-aligned, being processed following the same lithography step, where the second level includes third transistors, and where the third transistors are aligned to the alignment marks.

In another aspect, a 3D semiconductor device, the device including: a first level including a first single crystal layer and first transistors, where the first transistors each include a single crystal channel; first metal layers interconnecting at least the first transistors; alignment marks, where the first level includes the alignment marks; and a second level including a second single crystal layer and second transistors, where the second level overlays the first level, where the second transistors are horizontally oriented and each include at least two side gates, where the second level is bonded to the first level, where the bonded includes oxide to oxide bonds, and where the second transistors are aligned to the alignment marks.

In another aspect, a 3D semiconductor device, the device including: a first level including a first single crystal layer and first transistors, where the first transistors each include a single crystal channel; first metal layers interconnecting at least the first transistors; and a second level including a second single crystal layer and second transistors, where the second level overlays the first level, where the second transistors are horizontally oriented and include replacement gate, where the second level is bonded to the first level, and where the bonded includes oxide to oxide bonds.

In another aspect, a 3D semiconductor device, the device including: a first level including a first single crystal layer and alignment marks; first transistors overlaying the first single crystal layer; and second transistors overlaying the first transistors, where the first transistors and the second transistors are self-aligned, being processed following the same lithography step, where the second transistors include replacement gate, being processed to replace a poly silicon gate to a metal based gate, where the first level includes third transistors disposed below the first transistor, where the third transistors are aligned to the alignment marks, and where the third transistors each include a single crystal channel.

In another aspect, a 3D semiconductor device, the device including: a first level including a first single crystal layer, first transistors, and second transistors, where the second transistors are overlaying the first transistors, and where the first transistors and the second transistors are self-aligned, being processed following the same lithography step; and a second level including a second single crystal layer and third transistors, where the second level overlays the first level, where the third transistors are horizontally oriented and include replacement gate, where the second level is bonded to the first level, and where the bonded includes oxide to oxide bonds.

In another aspect, a 3D semiconductor device, the device including: a first level including a single crystal layer, a first metal layer, a second metal layer above the first metal layer, and a third metal layer above the second metal layer, where the second metal layer is significantly thicker than either the third metal layer or the first metal layer, where the third metal layer is precisely aligned to the first metal layer with less than 20 nm misalignment; a second level including a first array of first memory cells, each of the first memory cells include first transistors; and a third level including a second array of second memory cells, each of the second memory cells include second transistors, where the second level is above the third level, where the second transistors are self-aligned to the first transistors, being processed following the same lithography step, where the first level includes third transistors, where the first metal layer provides connections to the third transistors for the construction of periphery circuits, where connections from the periphery circuits to the first memory cells and the second memory cells include the second metal, the periphery circuits and the second metal are adapted to control the memory cells, and where the periphery circuits are directly underneath the first memory cells and the second memory cells.

In another aspect, a 3D semiconductor device, the device including: a first level including a single crystal layer, a first metal layer, a second metal layer above the first metal layer, and a third metal layer above the second metal layer, where the second metal layer has a significantly greater current carrying capacity than either the third metal layer or the first metal layer, where the third metal layer is precisely aligned to the first metal layer with less than 20 nm misalignment; a second level including a first array of first memory cells, each of the first memory cells include first transistors; a third level including a second array of second memory cells, each of the second memory cells include second transistors, where the second level is above the third level, where the second transistors are self-aligned to the first transistors, being processed following the same lithography step; and a fourth level including periphery circuits, the periphery circuits include connections by the second metal, where the periphery circuits are adapted to control the first memory cells and the second memory cells, and where the periphery circuits are atop the first memory cells and the second memory cells.

In another aspect, a 3D semiconductor device, the device including: a first level including a single crystal layer, a first metal layer, a second metal layer above the first metal layer, and a third metal layer above the second metal layer, where the second metal layer is significantly thicker than either the third metal layer or the first metal layer, where the third metal layer is precisely aligned to the first metal layer with less than 20 nm misalignment; a second level including a first array of first memory cells, each of the first memory cells include first transistors; a third level including a second array of second memory cells, each of the second memory cells include second transistors, where the second level is above the third level, where the second transistors are self-aligned to the first transistors, being processed following the same lithography step; and periphery circuits connected by the second metal to control the memory cells, where the periphery circuits are either underneath the memory cells or atop the memory cells.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which:

FIGS. 1A-1C show different types of junction-less transistors (JLT) that could be utilized for 3D stacking;

FIGS. 2A-2K show a zero-mask per layer 3D floating body DRAM;

FIGS. 3A-3J show a zero-mask per layer 3D resistive memory with a junction-less transistor;

FIGS. 4A-4K show an alternative zero-mask per layer 3D resistive memory;

FIGS. 5A-5G show a zero-mask per layer 3D charge-trap memory;

FIGS. 6A-6B show periphery on top of memory layers;

FIGS. 7A-7E show polysilicon select devices for 3D memory and peripheral circuits at the bottom according to some embodiments of the current invention;

FIGS. 8A-8F show polysilicon select devices for 3D memory and peripheral circuits at the top according to some embodiments of the current invention;

FIGS. 9A-9F illustrate a process flow for 3D integrated circuits with gate-last high-k metal gate transistors and face-up layer transfer;

FIGS. 10A-10D depict a process flow for constructing 3D integrated chips and circuits with misalignment tolerance techniques and repeating pattern in one direction;

FIGS. 11A-11G illustrate using a carrier wafer for layer transfer;

FIGS. 12A-12K illustrate constructing chips with nMOS and pMOS devices on either side of the wafer; and

FIG. 13 illustrates constructing transistors with front gates and back gates on either side of the semiconductor layer.

DETAILED DESCRIPTION

Embodiments of the present invention are now described with reference to FIGS. 1A-13, it being appreciated that the figures illustrate the subject matter not to scale or to measure. Many figures describe process flows for building devices. These process flows, which are essentially a sequence of steps for building a device, have many structures, numerals and labels that are common between two or more adjacent steps. In such cases, some labels, numerals and structures used for a certain step's figure may have been described in previous steps' figures.

FIG. 1A-1D shows that JLTs that can be 3D stacked fall into four categories based on the number of gates they use: One-side gated JLTs as shown in FIG. 1A, two-side gated JLTs as shown in FIG. 1B, three-side gated JLTs as shown in FIG. 1C, and gate-all-around JLTs as shown in FIG. 1D. The JLTS shown may include n+Si 102, gate dielectric 104, gate electrode 106, n+ source region 108, n+ drain region 110, and n+ region under gate 112. As the number of JLT gates increases, the gate gets more control of the channel, thereby reducing leakage of the JLT at 0V. Furthermore, the enhanced gate control can be traded-off for higher doping (which improves contact resistance to source-drain regions) or bigger JLT cross-sectional areas (which is easier from a process integration standpoint). However, adding more gates typically increases process complexity.

Some embodiments of this invention may involve floating body DRAM. Background information on floating body DRAM and its operation is given in “Floating Body RAM Technology and its Scalability to 32 nm Node and Beyond,” Electron Devices Meeting, 2006. IEDM '06. International, vol., no., pp. 1-4, 11-13 Dec. 2006 by T. Shino, N. Kusunoki, T. Higashi, et al., Overview and future challenges of floating body RAM (FBRAM) technology for 32 nm technology node and beyond, Solid-State Electronics, Volume 53, Issue 7, Papers Selected from the 38th European Solid-State Device Research Conference—ESSDERC'08, July 2009, Pages 676-683, ISSN 0038-1101, DOI: 10.1016/j.sse.2009.03.010 by Takeshi Hamamoto, Takashi Ohsawa, et al., “New Generation of Z-RAM,” Electron Devices Meeting, 2007. IEDM 2007. IEEE International, vol., no., pp. 925-928, 10-12 Dec. 2007 by Okhonin, S.; Nagoga, M.; Carman, E, et al. The above publications are incorporated herein by reference.

FIG. 2A-K describe a process flow to construct a horizontally-oriented monolithic 3D DRAM. This monolithic 3D DRAM utilizes the floating body effect and double-gate transistors. No mask is utilized on a “per-memory-layer” basis for the monolithic 3D DRAM concept shown in FIGS. 2A-K, and all other masks are shared between different layers. The process flow may include several steps in the following sequence.

Step (A): Peripheral circuits with tungsten wiring 202 are first constructed and above this a layer of silicon dioxide 204 is deposited. FIG. 2A shows a drawing illustration after Step (A).

Step (B): FIG. 2B illustrates the structure after Step (B). A wafer of p-Silicon 208 has an oxide layer 206 grown or deposited above it. Following this, hydrogen is implanted into the p-Silicon wafer at a certain depth indicated by 214. Alternatively, some other atomic species such as Helium could be (co-)implanted. This hydrogen implanted p-Silicon wafer 208 forms the top layer 210. The bottom layer 212 may include the peripheral circuits 202 with oxide layer 204. The top layer 210 is flipped and bonded to the bottom layer 212 using oxide-to-oxide bonding. Step (C): FIG. 2C illustrates the structure after Step (C). The stack of top and bottom wafers after Step (B) is cleaved at the hydrogen plane 3014 using either a anneal or a sideways mechanical force or other means. A CMP process is then conducted. A layer of silicon oxide 218 is then deposited atop the p-Silicon layer 216. At the end of this step, a single-crystal p-Si layer 216 exists atop the peripheral circuits, and this has been achieved using layer-transfer techniques. Step (D): FIG. 2D illustrates the structure after Step (D). Using methods similar to Step (B) and (C), multiple p-silicon layers 220 are formed with silicon oxide layers in between. Step (E): FIG. 2E illustrates the structure after Step (E). Lithography and etch processes are then utilized to make a structure as shown in the figure, including layer regions of p-silicon 221 and associated isolation/bonding oxides 222. Step (F): FIG. 2F illustrates the structure after Step (F). Gate dielectric 226 and gate electrode 224 are then deposited following which a CMP is done to planarize the gate electrode 224 regions. Lithography and etch are utilized to define gate regions. Step (G): FIG. 2G illustrates the structure after Step (G). Using the hard mask defined in Step (F), p-regions not covered by the gate are implanted to form n+ silicon regions 228. Spacers are utilized during this multi-step implantation process and layers of silicon present in different layers of the stack have different spacer widths to account for lateral straggle of buried layer implants. Bottom layers could have larger spacer widths than top layers. A thermal annealing step, such as a RTA or spike anneal or laser anneal or flash anneal, is then conducted to activate n+ doped regions. Step (H): FIG. 2H illustrates the structure after Step (H). A silicon oxide layer 230 is then deposited and planarized. For clarity, the silicon oxide layer is shown transparent, along with word-line (WL) 232 and source-line (SL) 234 regions. Step (I): FIG. 2I illustrates the structure after Step (I). Bit-line (BL) contacts 236 are formed by etching and deposition. These BL contacts are shared among all layers of memory. Step (J): FIG. 2J illustrates the structure after Step (J). BLs 238 are then constructed. Contacts are made to BLs, WLs and SLs of the memory array at its edges. SL contacts can be made into stair-like structures using techniques described in “Bit Cost Scalable Technology with Punch and Plug Process for Ultra High Density Flash Memory,” VLSI Technology, 2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun. 2007 by Tanaka, H.; Kido, M.; Yahashi, K.; Oomura, M.; et al., following which contacts can be constructed to them. Formation of stair-like structures for SLs could be done in steps prior to Step (J) as well. FIG. 2K shows cross-sectional views of the array for clarity. Double-gated transistors may be utilized along with the floating body effect for storing information. A floating-body DRAM has thus been constructed, with (1) horizontally-oriented transistors—i.e. current flowing in substantially the horizontal direction in transistor channels (2) some of the memory cell control lines, e.g., source-lines SL, constructed of heavily doped silicon and embedded in the memory cell layer, (3) side gates simultaneously deposited over multiple memory layers, and (4) monocrystalline (or single-crystal) silicon layers obtained by layer transfer techniques such as ion-cut.

With the explanations for the formation of monolithic 3D DRAM with ion-cut in this section, it is clear to one skilled in the art that alternative implementations are possible. BL and SL nomenclature has been used for two terminals of the 3D DRAM array, and this nomenclature can be interchanged. Each gate of the double gate 3D DRAM can be independently controlled for better control of the memory cell. To implement these changes, the process steps in FIG. 2 may be modified. Moreover, selective epi technology or laser recrystallization technology could be utilized for implementing structures shown in FIG. 2A-K. Various other types of layer transfer schemes that have been described in Section 1.3.4 of the parent application (Ser. No. 12/901,890, 8,026,521) can be utilized for construction of various 3D DRAM structures. Furthermore, buried wiring, i.e. where wiring for memory arrays is below the memory layers but above the periphery, may also be used. In addition, other variations of the monolithic 3D DRAM concepts are possible.

While many of today's memory technologies rely on charge storage, several companies are developing non-volatile memory technologies based on resistance of a material changing. Examples of these resistance-based memories include phase change memory, Metal Oxide memory, resistive RAM (RRAM), memristors, solid-electrolyte memory, ferroelectric RAM, MRAM, etc. Background information on these resistive-memory types is given in “Overview of candidate device technologies for storage-class memory,” IBM Journal of Research and Development, vol. 52, no. 4.5, pp. 449-464, July 2008 by Burr, G. W.; Kurdi, B. N.; Scott, J. C.; Lam, C. H.; Gopalakrishnan, K.; Shenoy, R. S.

FIGS. 3A-J describe a novel memory architecture for resistance-based memories, and a procedure for its construction. The memory architecture utilizes junction-less transistors and has a resistance-based memory element in series with a transistor selector. No mask is utilized on a “per-memory-layer” basis for the monolithic 3D resistance change memory (or resistive memory) concept shown in FIGS. 3A-J, and all other masks are shared between different layers. The process flow may include several steps that occur in the following sequence.

Step (A): Peripheral circuits 302 are first constructed and above this a layer of silicon dioxide 304 is deposited. FIG. 3A shows a drawing illustration after Step (A).

Step (B): FIG. 3B illustrates the structure after Step (B). A wafer of n+ Silicon 308 has an oxide layer 306 grown or deposited above it. Following this, hydrogen is implanted into the n+ Silicon wafer at a certain depth indicated by 314. Alternatively, some other atomic species such as Helium could be (co-)implanted. This hydrogen implanted n+ Silicon wafer 308 forms the top layer 310. The bottom layer 312 may include the peripheral circuits 302 with oxide layer 304. The top layer 310 is flipped and bonded to the bottom layer 312 using oxide-to-oxide bonding. Step (C): FIG. 3C illustrates the structure after Step (C). The stack of top and bottom wafers after Step (B) is cleaved at the hydrogen plane 314 using either an anneal or a sideways mechanical force or other means. A CMP process is then conducted. A layer of silicon oxide 318 is then deposited atop the n+ Silicon layer 316. At the end of this step, a single-crystal n+Si layer 316 exists atop the peripheral circuits, and this has been achieved using layer-transfer techniques. Step (D): FIG. 3D illustrates the structure after Step (D). Using methods similar to Step (B) and (C), multiple n+ silicon layers 320 are formed with silicon oxide layers in between. Step (E): FIG. 3E illustrates the structure after Step (E). Lithography and etch processes are then utilized to make a structure as shown in the figure, including layer regions of n+ silicon 321 and associated bonding/isolation oxides 322. Step (F): FIG. 3F illustrates the structure after Step (F). Gate dielectric 326 and gate electrode 324 are then deposited following which a CMP is performed to planarize the gate electrode 324 regions. Lithography and etch are utilized to define gate regions. Step (G): FIG. 3G illustrates the structure after Step (G). A silicon oxide layer 330 is then deposited and planarized. The silicon oxide layer is shown transparent in the figure for clarity, along with word-line (WL) 332 and source-line (SL) 334 regions. Step (H): FIG. 3H illustrates the structure after Step (H). Vias are etched through multiple layers of silicon and silicon dioxide as shown in the figure. A resistance change memory material 336 is then deposited (preferably with atomic layer deposition (ALD)). Examples of such a material include hafnium oxide, well known to change resistance by applying voltage. An electrode for the resistance change memory element is then deposited (preferably using ALD) and is shown as electrode/BL contact 340. A CMP process is then conducted to planarize the surface. It can be observed that multiple resistance change memory elements in series with junctionless transistors are created after this step. Step (I): FIG. 3I illustrates the structure after Step (I). BLs 338 are then constructed. Contacts are made to BLs, WLs and SLs of the memory array at its edges. SL contacts can be made into stair-like structures using techniques described in in “Bit Cost Scalable Technology with Punch and Plug Process for Ultra High Density Flash Memory,” VLSI Technology, 2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun. 2007 by Tanaka, H.; Kido, M.; Yahashi, K.; Oomura, M.; et al., following which contacts can be constructed to them. Formation of stair-like structures for SLs could be achieved in steps prior to Step (I) as well. FIG. 3J shows cross-sectional views of the array for clarity. A 3D resistance change memory has thus been constructed, with (1) horizontally-oriented transistors—i.e. current flowing in substantially the horizontal direction in transistor channels, (2) some of the memory cell control lines, e.g., source-lines SL, constructed of heavily doped silicon and embedded in the memory cell layer, (3) side gates that are simultaneously deposited over multiple memory layers for transistors, and (4) monocrystalline (or single-crystal) silicon layers obtained by layer transfer techniques such as ion-cut.

FIGS. 4A-4K describe an alternative process flow to construct a horizontally-oriented monolithic 3D resistive memory array. This embodiment has a resistance-based memory element in series with a transistor selector. No mask is utilized on a “per-memory-layer” basis for the monolithic 3D resistance change memory (or resistive memory) concept shown in FIGS. 4A-4K, and all other masks are shared between different layers. The process flow may include several steps as described in the following sequence.

Step (A): Peripheral circuits with tungsten wiring 402 are first constructed and above this a layer of silicon dioxide 404 is deposited. FIG. 4A shows a drawing illustration after Step (A).

Step (B): FIG. 4B illustrates the structure after Step (B). A wafer of p-Silicon 408 has an oxide layer 406 grown or deposited above it. Following this, hydrogen is implanted into the p-Silicon wafer at a certain depth indicated by 414. Alternatively, some other atomic species such as Helium could be (co-)implanted. This hydrogen implanted p-Silicon wafer 408 forms the top layer 410. The bottom layer 412 may include the peripheral circuits 402 with oxide layer 404. The top layer 410 is flipped and bonded to the bottom layer 412 using oxide-to-oxide bonding. Step (C): FIG. 4C illustrates the structure after Step (C). The stack of top and bottom wafers after Step (B) is cleaved at the hydrogen plane 414 using either a anneal or a sideways mechanical force or other means. A CMP process is then conducted. A layer of silicon oxide 418 is then deposited atop the p-Silicon layer 416. At the end of this step, a single-crystal p-Si layer 416 exists atop the peripheral circuits, and this has been achieved using layer-transfer techniques. Step (D): FIG. 4D illustrates the structure after Step (D). Using methods similar to Step (B) and (C), multiple p-silicon layers 420 are formed with silicon oxide layers in between. Step (E): FIG. 4E illustrates the structure after Step (E). Lithography and etch processes are then utilized to make a structure as shown in the figure, including layer regions of p-silicon 421 and associated bonding/isolation oxide 422. Step (F): FIG. 4F illustrates the structure on after Step (F). Gate dielectric 426 and gate electrode 424 are then deposited following which a CMP is done to planarize the gate electrode 424 regions. Lithography and etch are utilized to define gate regions. Step (G): FIG. 4G illustrates the structure after Step (G). Using the hard mask defined in Step (F), p-regions not covered by the gate are implanted to form n+ silicon regions 428. Spacers are utilized during this multi-step implantation process and layers of silicon present in different layers of the stack have different spacer widths to account for lateral straggle of buried layer implants. Bottom layers could have larger spacer widths than top layers. A thermal annealing step, such as a RTA or spike anneal or laser anneal or flash anneal, is then conducted to activate n+ doped regions. Step (H): FIG. 4H illustrates the structure after Step (H). A silicon oxide layer 430 is then deposited and planarized. The silicon oxide layer is shown transparent in the figure for clarity, along with word-line (WL) 432 and source-line (SL) 434 regions. Step (I): FIG. 4I illustrates the structure after Step (I). Vias are etched through multiple layers of silicon and silicon dioxide as shown in the figure. A resistance change memory material 436 is then deposited (preferably with atomic layer deposition (ALD)). Examples of such a material include hafnium oxide, which is well known to change resistance by applying voltage. An electrode for the resistance change memory element is then deposited (preferably using ALD) and is shown as electrode/BL contact 440. A CMP process is then conducted to planarize the surface. It can be observed that multiple resistance change memory elements in series with transistors are created after this step. Step (J): FIG. 4J illustrates the structure after Step (J). BLs 438 are then constructed. Contacts are made to BLs, WLs and SLs of the memory array at its edges. SL contacts can be made into stair-like structures using techniques described in “Bit Cost Scalable Technology with Punch and Plug Process for Ultra High Density Flash Memory,” VLSI Technology, 2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun. 2007 by Tanaka, H.; Kido, M.; Yahashi, K.; Oomura, M.; et al., following which contacts can be constructed to them. Formation of stair-like structures for SLs could be done in steps prior to Step (I) as well. FIG. 4K shows cross-sectional views of the array for clarity. A 3D resistance change memory has thus been constructed, with (1) horizontally-oriented transistors—i.e. current flowing in substantially the horizontal direction in transistor channels, (2) some of the memory cell control lines—e.g., source-lines SL, constructed of heavily doped silicon and embedded in the memory cell layer, (3) side gates simultaneously deposited over multiple memory layers for transistors, and (4) monocrystalline (or single-crystal) silicon layers obtained by layer transfer techniques such as ion-cut.

While explanations have been given for formation of monolithic 3D resistive memories with ion-cut in this section, it is clear to one skilled in the art that alternative implementations are possible. BL and SL nomenclature has been used for two terminals of the 3D resistive memory array, and this nomenclature can be interchanged. Moreover, selective epi technology or laser recrystallization technology could be utilized for implementing structures shown in FIGS. 3A-3J and FIGS. 4A-4K. Various other types of layer transfer schemes that have been described in Section 1.3.4 of the parent application can be utilized for construction of various 3D resistive memory structures. One could also use buried wiring, i.e. where wiring for memory arrays is below the memory layers but above the periphery. Other variations of the monolithic 3D resistive memory concepts are possible.

While resistive memories described previously form a class of non-volatile memory, others classes of non-volatile memory exist. NAND flash memory forms one of the most common non-volatile memory types. It can be constructed of two main types of devices: floating-gate devices where charge is stored in a floating gate and charge-trap devices where charge is stored in a charge-trap layer such as Silicon Nitride. Background information on charge-trap memory can be found in “Integrated Interconnect Technologies for 3D Nanoelectronic Systems”, Artech House, 2009 by Bakir and Meindl (“Bakir”) and “A Highly Scalable 8-Layer 3D Vertical-Gate (VG) TFT NAND Flash Using Junction-Free Buried Channel BE-SONOS Device,” Symposium on VLSI Technology, 2010 by Hang-Ting Lue, et al. The architectures shown in FIG. 5A-5G are relevant for any type of charge-trap memory.

FIGS. 5A-5G describes a memory architecture for single-crystal 3D charge-trap memories, and a procedure for its construction. It utilizes junction-less transistors. No mask is utilized on a “per-memory-layer” basis for the monolithic 3D charge-trap memory concept shown in FIGS. 5A-5G, and all other masks are shared between different layers. The process flow may include several steps as described in the following sequence.

Step (A): Peripheral circuits 502 are first constructed and above this a layer of silicon dioxide 504 is deposited. FIG. 5A shows a drawing illustration after Step (A).

Step (B): FIG. 5B illustrates the structure after Step (B). A wafer of n+ Silicon 508 has an oxide layer 506 grown or deposited above it. Following this, hydrogen is implanted into the n+ Silicon wafer at a certain depth indicated by 514. Alternatively, some other atomic species such as Helium could be implanted. This hydrogen implanted n+ Silicon wafer 508 forms the top layer 510. The bottom layer 512 may include the peripheral circuits 502 with oxide layer 504. The top layer 510 is flipped and bonded to the bottom layer 512 using oxide-to-oxide bonding. Step (C): FIG. 5C illustrates the structure after Step (C). The stack of top and bottom wafers after Step (B) is cleaved at the hydrogen plane 514 using either a anneal or a sideways mechanical force or other means. A CMP process is then conducted. A layer of silicon oxide 518 is then deposited atop the n+ Silicon layer 516. At the end of this step, a single-crystal n+Si layer 516 exists atop the peripheral circuits, and this has been achieved using layer-transfer techniques. Step (D): FIG. 5D illustrates the structure after Step (D). Using methods similar to Step (B) and (C), multiple n+ silicon layers 520 are formed with silicon oxide layers in between. Step (E): FIG. 5E illustrates the structure after Step (E). Lithography and etch processes are then utilized to make a structure as shown in the figure. Step (F): FIG. 5F illustrates the structure after Step (F). Gate dielectric 526 and gate electrode 524 are then deposited following which a CMP is done to planarize the gate electrode 524 regions. Lithography and etch are utilized to define gate regions. Gates of the NAND string 536 as well gates of select gates of the NAND string 538 are defined. Step (G): FIG. 5G illustrates the structure after Step (G). A silicon oxide layer 530 is then deposited and planarized. It is shown transparent in the figure for clarity. Word-lines, bit-lines and source-lines are defined as shown in the figure. Contacts are formed to various regions/wires at the edges of the array as well. SL contacts can be made into stair-like structures using techniques described in “Bit Cost Scalable Technology with Punch and Plug Process for Ultra High Density Flash Memory,” VLSI Technology, 2007 IEEE Symposium on, vol., no., pp. 14-15, 12-14 Jun. 2007 by Tanaka, H.; Kido, M.; Yahashi, K.; Oomura, M.; et al., following which contacts can be constructed to them. Formation of stair-like structures for SLs could be performed in steps prior to Step (G) as well. A 3D charge-trap memory has thus been constructed, with (1) horizontally-oriented transistors—i.e. current flowing in substantially the horizontal direction in transistor channels, (2) some of the memory cell control lines—e.g., bit lines BL, constructed of heavily doped silicon and embedded in the memory cell layer, (3) side gates simultaneously deposited over multiple memory layers for transistors, and (4) monocrystalline (or single-crystal) silicon layers obtained by layer transfer techniques such as ion-cut. This use of single-crystal silicon obtained with ion-cut is a key differentiator from past work on 3D charge-trap memories such as “A Highly Scalable 8-Layer 3D Vertical-Gate (VG) TFT NAND Flash Using Junction-Free Buried Channel BE-SONOS Device,” Symposium on VLSI Technology, 2010 by Hang-Ting Lue, et al. that used polysilicon.

While FIGS. 5A-5G give two examples of how single-crystal silicon layers with ion-cut can be used to produce 3D charge-trap memories, the ion-cut technique for 3D charge-trap memory is fairly general. It could be utilized to produce any horizontally-oriented 3D monocrystalline-silicon charge-trap memory.

While the 3D DRAM and 3D resistive memory implementations in Section 3 and Section 4 have been described with single crystal silicon constructed with ion-cut technology, other options exist. One could construct them with selective epi technology. Procedures for doing these will be clear to those skilled in the art.

FIGS. 6A-6B show it is not the only option for the architecture to have the peripheral transistors, such as periphery 602, below the memory layers, including, for example, memory layer 604, memory layer 606, and/or memory layer 608. Peripheral transistors, such as periphery 610, could also be constructed above the memory layers, including, for example, memory layer 604, memory layer 606, and/or memory layer 608, and substrate or memory layer 612, as shown in FIG. 6B. This periphery layer would utilize technologies described in this application, and could utilize transistors, for example, junction-less transistors or recessed channel transistors.

The monolithic 3D integration concepts described in this patent application can lead to novel embodiments of poly-silicon-based memory architectures as well. Poly silicon based architectures could potentially be cheaper than single crystal silicon based architectures when a large number of memory layers need to be constructed. While the below concepts are explained by using resistive memory architectures as an example, it will be clear to one skilled in the art that similar concepts can be applied to NAND flash memory and DRAM architectures described previously in this patent application.

FIGS. 7A-7E show one embodiment of the current invention, where polysilicon junction-less transistors are used to form a 3D resistance-based memory. The utilized junction-less transistors can have either positive or negative threshold voltages. The process may include the following steps as described in the following sequence:

Step (A): As illustrated in FIG. 7A, peripheral circuits 702 are constructed above which a layer of silicon dioxide 704 is made.

Step (B): As illustrated in FIG. 7B, multiple layers of n+ doped amorphous silicon or polysilicon 706 are deposited with layers of silicon dioxide 708 in between. The amorphous silicon or polysilicon layers 706 could be deposited using a chemical vapor deposition process, such as LPCVD or PECVD. Step (C): As illustrated in FIG. 7C, a Rapid Thermal Anneal (RTA) is conducted to crystallize the layers of polysilicon or amorphous silicon deposited in Step (B). Temperatures during this RTA could be as high as 700° C. or more, and could even be as high as 800° C. The polysilicon region obtained after Step (C) is indicated as 710. Alternatively, a laser anneal could be conducted, either for all layers 706 at the same time or layer by layer. The thickness of the oxide 704 would need to be optimized if that process were conducted. Step (D): As illustrated in FIG. 7D, procedures similar to those described in FIGS. 3E-3H are utilized to construct the structure shown. The structure in FIG. 7D has multiple levels of junction-less transistor selectors for resistive memory devices. The resistance change memory is indicated as 736 while its electrode and contact to the BL is indicated as 740. The WL is indicated as 732, while the SL is indicated as 734. Gate dielectric of the junction-less transistor is indicated as 726 while the gate electrode of the junction-less transistor is indicated as 724, this gate electrode also serves as part of the WL 732. Silicon oxide is indicated as 730. Step (E): As illustrated in FIG. 7E, bit lines (indicated as BL 738) are constructed. Contacts are then made to peripheral circuits and various parts of the memory array as described in embodiments described previously.

FIG. 8A-F show another embodiment of the current invention, where polysilicon junction-less transistors are used to form a 3D resistance-based memory. The utilized junction-less transistors can have either positive or negative threshold voltages. The process may include the following steps occurring in sequence:

Step (A): As illustrated in FIG. 8A, a layer of silicon dioxide 804 is deposited or grown above a silicon substrate without circuits 802.

Step (B): As illustrated in FIG. 8B, multiple layers of n+ doped amorphous silicon or polysilicon 806 are deposited with layers of silicon dioxide 808 in between. The amorphous silicon or polysilicon layers 806 could be deposited using a chemical vapor deposition process, such as LPCVD or PECVD abbreviated as above. Step (C): As illustrated in FIG. 8C, a Rapid Thermal Anneal (RTA) or standard anneal is conducted to crystallize the layers of polysilicon or amorphous silicon deposited in Step (B). Temperatures during this RTA could be as high as 700° C. or more, and could even be as high as 1400° C. The polysilicon region obtained after Step (C) is indicated as 810. Since there are no circuits under these layers of polysilicon, very high temperatures (such as 1400° C.) can be used for the anneal process, leading to very good quality polysilicon with few grain boundaries and very high mobilities approaching those of single crystal silicon. Alternatively, a laser anneal could be conducted, either for all layers 806 at the same time or layer by layer at different times. Step (D): This is illustrated in FIG. 8D. Procedures similar to those described in FIG. 32E-H of U.S. Pat. No. 8,026,521, are utilized to obtain the structure shown in FIG. 8D which has multiple levels of junctionless transistor selectors for resistive memory devices. The resistance change memory is indicated as 836 while its electrode and contact to the BL is indicated as 840. The WL is indicated as 832, while the SL is indicated as 834. Gate dielectric of the junction-less transistor is indicated as 826 while the gate electrode of the junction-less transistor is indicated as 824, this gate electrode also serves as part of the WL 832. Silicon oxide is indicated as 830 Step (E): This is illustrated in FIG. 8E. Bit lines (indicated as BL 838) are constructed. Contacts are then made to peripheral circuits and various parts of the memory array as described in embodiments described previously. Step (F): Using procedures described in Section 1 and Section 2 of this patent application's parent, peripheral circuits 898 (with transistors and wires) could be formed well aligned to the multiple memory layers shown in Step (E). For the periphery, one could use the process flow shown in Section 2 where replacement gate processing is used, or one could use sub-400° C. processed transistors such as junction-less transistors or recessed channel transistors. Alternatively, one could use laser anneals for peripheral transistors' source-drain processing. Various other procedures described in Section 1 and Section 2 could also be used. Connections can then be formed between the multiple memory layers and peripheral circuits. By proper choice of materials for memory layer transistors and memory layer wires (e.g., by using tungsten and other materials that withstand high temperature processing for wiring), even standard transistors processed at high temperatures (>1000° C.) for the periphery could be used.

Section 1, of U.S. Pat. No. 8,026,521, described the formation of 3D stacked semiconductor circuits and chips with sub-400° C. processing temperatures to build transistors and high density of vertical connections. In this section an alternative method is explained, in which a transistor is built with any replacement gate (or gate-last) scheme that is utilized widely in the industry. This method allows for high temperatures (above 400 C) to build the transistors. This method utilizes a combination of three concepts:

-   -   Replacement gate (or gate-last) high k/metal gate fabrication     -   Face-up layer transfer using a carrier wafer     -   Misalignment tolerance techniques that utilize regular or         repeating layouts. In these repeating layouts, transistors could         be arranged in substantially parallel bands.         A very high density of vertical connections is possible with         this method. Single crystal silicon (or monocrystalline silicon)         layers that are transferred are less than 2 um thick, or could         even be thinner than 0.4 um or 0.2 um.

The method mentioned in the previous paragraph is described in FIG. 9A-9F. The procedure may include several steps as described in the following sequence:

Step (A): After creating isolation regions using a shallow-trench-isolation (STI) process 2504, dummy gates 2502 are constructed with silicon dioxide and poly silicon. The term “dummy gates” is used since these gates will be replaced by high k gate dielectrics and metal gates later in the process flow, according to the standard replacement gate (or gate-last) process. Further details of replacement gate processes are described in “A 45 nm Logic Technology with High-k+Metal Gate Transistors, Strained Silicon, 9 Cu Interconnect Layers, 193 nm Dry Patterning, and 100% Pb-free Packaging,” IEDM Tech. Dig., pp. 247-250, 2007 by K. Mistry, et al. and “Ultralow-EOT (5 Å) Gate-First and Gate-Last High Performance CMOS Achieved by Gate-Electrode Optimization,” IEDM Tech. Dig., pp. 663-666, 2009 by L. Ragnarsson, et al. FIG. 9A illustrates the structure after Step (A).

Step (B): Rest of the transistor fabrication flow proceeds with formation of source-drain regions 2506, strain enhancement layers to improve mobility, high temperature anneal to activate source-drain regions 2506, formation of inter-layer dielectric (ILD) 2508, etc. FIG. 9B illustrates the structure after Step (B).

Step (C): Hydrogen is implanted into the wafer at the dotted line regions indicated by 2510. FIG. 9C illustrates the structure after Step (C).

Step (D): The wafer after step (C) is bonded to a temporary carrier wafer 2512 using a temporary bonding adhesive 2514. This temporary carrier wafer 2512 could be constructed of glass. Alternatively, it could be constructed of silicon. The temporary bonding adhesive 2514 could be a polymer material, such as a polyimide. A anneal or a sideways mechanical force is utilized to cleave the wafer at the hydrogen plane 2510. A CMP process is then conducted. FIG. 9D illustrates the structure after Step (D).

Step (E): An oxide layer 2520 is deposited onto the bottom of the wafer shown in Step (D). The wafer is then bonded to the bottom layer of wires and transistors 2522 using oxide-to-oxide bonding. The bottom layer of wires and transistors 2522 could also be called a base wafer. The temporary carrier wafer 2512 is then removed by shining a laser onto the temporary bonding adhesive 2514 through the temporary carrier wafer 2512 (which could be constructed of glass). Alternatively, an anneal could be used to remove the temporary bonding adhesive 2514. Through-silicon connections 2516 with a non-conducting (e.g. oxide) liner 2515 to the landing pads 2518 in the base wafer could be constructed at a very high density using special alignment methods described in at least FIGS. 26A-D and FIGS. 27A-F of U.S. Pat. No. 8,026,521. FIG. 9E illustrates the structure after Step (E).

Step (F): Dummy gates 2502 are etched away, followed by the construction of a replacement with high k gate dielectrics 2524 and metal gates 2526. Essentially, partially-formed high performance transistors are layer transferred atop the base wafer (may also be called target wafer) followed by the completion of the transistor processing with a low (sub 400° C.) process. FIG. 9F illustrates the structure after Step (F). The remainder of the transistor, contact, and wiring layers are then constructed.

It will be obvious to someone skilled in the art that alternative versions of this flow are possible with various methods to attach temporary carriers and with various versions of the gate-last process flow.

FIGS. 10A-10D (and FIG. 45A-D of U.S. Pat. No. 8,026,521) show an alternative procedure for forming CMOS circuits with a high density of connections between stacked layers. The process utilizes a repeating pattern in one direction for the top layer of transistors. The procedure may include several steps in the following sequence:

Step (A): Using procedures similar to FIG. 9A-F, a top layer of transistors 4404 is transferred atop a bottom layer of transistors and wires 4402. Landing pads 4406 are utilized on the bottom layer of transistors and wires 4402. Dummy gates 4408 and 4410 are utilized for nMOS and pMOS. The key difference between the structures shown in FIGS. 9A-F and this structure is the layout of oxide isolation regions between transistors. FIG. 10A illustrates the structure after Step (A).

Step (B): Through-silicon connections 4412 are formed well-aligned to the bottom layer of transistors and wires 4402. Alignment schemes to be described in FIG. 45A-D of U.S. Pat. No. 8,026,521 are utilized for this purpose. All features constructed in future steps are also formed well-aligned to the bottom layer of transistors and wires 4402. FIG. 10B illustrates the structure after Step (B).

Step (C): Oxide isolation regions 4414 are formed between adjacent transistors to be defined. These isolation regions are formed by lithography and etch of gate and silicon regions and then fill with oxide. FIG. 10C illustrates the structure after Step (C).

Step (D): The dummy gates 4408 and 4410 are etched away and replaced with replacement gates 4416 and 4418. These replacement gates are patterned and defined to form gate contacts as well. FIG. 10D illustrates the structure after Step (D). Following this, other process steps in the fabrication flow proceed as usual.

FIGS. 11A-11G illustrate using a carrier wafer for layer transfer. FIG. 11A illustrates the first step of preparing transistors with dummy gates 4602 on first donor wafer (or top wafer) 4606. This completes the first phase of transistor formation.

FIG. 11B illustrates forming a cleave line 4608 by implant 4616 of atomic particles such as H+. FIG. 11C illustrates permanently bonding the first donor wafer 4606 to a second donor wafer 4626. The permanent bonding may be oxide to oxide wafer bonding as described previously.

FIG. 11D illustrates the second donor wafer 4626 acting as a carrier wafer after cleaving the first donor wafer off potentially at face 4632; leaving a thin layer 4606 with the now buried dummy gate transistors 4602. FIG. 11E illustrates forming a second cleave line 4618 in the second donor wafer 4626 by implant 4646 of atomic species such as H+.

FIG. 11F illustrates the second layer transfer step to bring the dummy gate transistors 4602 ready to be permanently bonded on top of the bottom layer of transistors and wires 4601. For the simplicity of the explanation we left out the now obvious steps of surface layer preparation done for each of these bonding steps.

FIG. 11G illustrates the bottom layer of transistors and wires 4601 with the dummy gate transistor 4602 on top after cleaving off the second donor wafer and removing the layers on top of the dummy gate transistors. Now we can proceed and replace the dummy gates with the final gates, form the metal interconnection layers, and continue the 3D fabrication process.

An interesting alternative is available when using the carrier wafer flow described in FIG. 11A-11G. In this flow we can use the two sides of the transferred layer to build NMOS on one side and PMOS on the other side. Timing properly the replacement gate step such flow could enable full performance transistors properly aligned to each other. As illustrated in FIG. 12A, an SOI (Silicon On Insulator) donor (or top) wafer 4700 may be processed in the normal state of the art high k metal gate gate-last manner with adjusted thermal cycles to compensate for later thermal processing up to the step prior to where CMP exposure of the polysilicon dummy gates 4704 takes place. FIG. 12A illustrates a cross section of the SOI donor wafer substrate 4700, the buried oxide (BOX) 4701, the thin silicon layer 4702 of the SOI wafer, the isolation 4703 between transistors, the polysilicon 4704 and gate oxide 4705 of n-type CMOS transistors with dummy gates, their associated source and drains 4706 for NMOS, NMOS transistor channel regions 4707, and the NMOS interlayer dielectric (ILD) 4708. Alternatively, the PMOS device may be constructed at this stage. This completes the first phase of transistor formation.

At this step, or alternatively just after a CMP of layer 4708 to expose the polysilicon dummy gates 4704 or to planarize the oxide layer 4708 and not expose the dummy gates 4704, an implant of an atomic species 4710, such as H+, is done to prepare the cleaving plane 4712 in the bulk of the donor substrate, as illustrated in FIG. 12B.

The SOI donor wafer 4700 is now permanently bonded to a carrier wafer 4720 that has been prepared with an oxide layer 4716 for oxide to oxide bonding to the donor wafer surface 4714 as illustrated in FIG. 12C. The details have been described previously. The donor wafer 4700 may then be cleaved at the cleaving plane 4712 and may be thinned by chemical mechanical polishing (CMP) and surface 4722 may be prepared for transistor formation. The donor wafer layer 4700 at surface 4722 may be processed in the normal state of the art gate last processing to form the PMOS transistors with dummy gates. During processing the wafer is flipped so that surface 4722 is on top, but for illustrative purposes this is not shown in the subsequent FIGS. 12E-12G.

FIG. 12E illustrates the cross section with the buried oxide (BOX) 4701, the now thin silicon layer 4700 of the SOI substrate, the isolation 4733 between transistors, the polysilicon 4734 and gate oxide 4735 of p-type CMOS dummy gates, their associated source and drains 4736 for PMOS, PMOS transistor channel regions 4737 and the PMOS interlayer dielectric (ILD) 4738. The PMOS transistors may be precisely aligned at state of the art tolerances to the NMOS transistors due to the shared substrate 4700 possessing the same alignment marks. At this step, or alternatively just after a CMP of layer 4738 to expose the PMOS polysilicon dummy gates or to planarize the oxide layer 4738 and not expose the dummy gates, the wafer could be put into high temperature cycle to activate both the dopants in the NMOS and the PMOS source drain regions.

Then an implant of an atomic species 4740, such as H+, may prepare the cleaving plane 4721 in the bulk of the carrier wafer substrate 4720 for layer transfer suitability, as illustrated in FIG. 12F. The PMOS transistors are now ready for normal state of the art gate-last transistor formation completion.

As illustrated in FIG. 12G, the inter layer dielectric 4738 may be chemical mechanically polished to expose the top of the polysilicon dummy gates 4734. The dummy polysilicon gates 4734 may then be removed by etch and the PMOS hi-k gate dielectric 4740 and the PMOS specific work function metal gate 4741 may be deposited. An aluminum fill 4742 may be performed on the PMOS gates and the metal CMP′ed. A dielectric layer 4739 may be deposited and the normal gate 4743 and source/drain 4744 contact formation and metallization.

The PMOS layer to NMOS layer via 4747 and metallization may be partially formed as illustrated in FIG. 12G and an oxide layer 4748 is deposited to prepare for bonding.

The carrier wafer and two sided n/p layer is then permanently bonded to bottom wafer having transistors and wires 4799 with associated metal landing strip 4750 as illustrated in FIG. 12H.

The carrier wafer 4720 may then be cleaved at the cleaving plane 4721 and may be thinned by chemical mechanical polishing (CMP) to oxide layer 4716 as illustrated in FIG. 12I.

The NMOS transistors are now ready for normal state of the art gate-last transistor formation completion. As illustrated in FIG. 12J, the oxide layer 4716 and the NMOS inter layer dielectric 4708 may be chemical mechanically polished to expose the top of the NMOS polysilicon dummy gates 4704. The dummy polysilicon gates 4704 may then be removed by etch and the NMOS hi-k gate dielectric 4760 and the NMOS specific work function metal gate 4761 may be deposited. An aluminum fill 4762 may be performed on the NMOS gates and the metal CMP′ed. A dielectric layer 4769 may be deposited and the normal gate 4763 and source/drain 4764 contact formation and metallization. The NMOS layer to PMOS layer via 4767 to connect to 4747 and metallization may be formed.

As illustrated in FIG. 12K, the layer-to-layer contacts 4772 to the landing pads in the base wafer are now made. This same contact etch could be used to make the connections 4773 between the NMOS and PMOS layer as well, instead of using the two step (4747 and 4767) method in FIG. 12H.

Using procedures similar to FIG. 12A-K, it is possible to construct structures such as FIG. 13 where a transistor is constructed with front gate 4902 and back gate 4904. The back gate could be utilized for many purposes such as threshold voltage control, reduction of variability, increase of drive current and other purposes.

It will also be appreciated by persons of ordinary skill in the art that the invention is not limited to what has been particularly shown and described hereinabove. For example, drawings or illustrations may not show n or p wells for clarity in illustration. Further, combinations and sub-combinations of the various features described hereinabove may be utilized to form a 3D IC based system. Rather, the scope of the invention includes both combinations and sub-combinations of the various features described hereinabove as well as modifications and variations which would occur to such skilled persons upon reading the foregoing description. Thus the invention is to be limited only by the appended claims. 

What is claimed is:
 1. A 3D semiconductor device, the device comprising; a first level comprising a single crystal layer, a first metal layer, a second metal layer above said first metal layer, and a third metal layer above said second metal layer, wherein said second metal layer is significantly thicker than either said third metal layer or said first metal layer; a second level comprising a first array of first memory cells, each of said first memory cells comprise first transistors; and a third level comprising a second array of second memory cells, each of said second memory cells comprise second transistors, wherein said second level is above said third level, wherein said second transistors are self-aligned to said first transistors, being processed following a same lithography step, wherein said first level comprises third transistors, wherein said first metal layer provides connections to said third transistors for a construction of periphery circuits, wherein connections from said periphery circuits to said first memory cells and said second memory cells comprise said second metal, said periphery circuits and said second metal are adapted to control said first memory cells and said second memory cells, and wherein said periphery circuits are directly underneath said first memory cells and said second memory cells.
 2. The 3D semiconductor device according to claim 1, wherein at least one of said second transistors comprises a source, a channel, and a drain, and wherein said source, said channel, and said drain have a same dopant type.
 3. The 3D semiconductor device according to claim 1, wherein said first level comprises through silicon vias (TSVs) providing connections to an external device.
 4. The 3D semiconductor device according to claim 1, wherein said significantly thicker is at least 100% thicker.
 5. The 3D semiconductor device according to claim 1, wherein at least one of said first transistors comprises a source, a channel, and a drain, and wherein said source, said channel, and said drain have a same dopant type.
 6. The 3D semiconductor device according to claim 1, further comprising: a fourth level disposed above said second level, wherein said fourth level comprises a single crystal silicon layer.
 7. The 3D semiconductor device according to claim 1, further comprising: a fourth level disposed above said third level, wherein said fourth level comprises a single crystal silicon layer, and wherein said fourth level comprises through silicon vias (TSVs) providing connections to an external device.
 8. A 3D semiconductor device, the device comprising; a first level comprising a single crystal layer, a first metal layer, a second metal layer above said first metal layer, and a third metal layer above said second metal layer, wherein said second metal layer has a significantly greater current carrying capacity than either said third metal layer or said first metal layer; a second level comprising a first array of first memory cells, each of said first memory cells comprise first transistors; a third level comprising a second array of second memory cells, each of said second memory cells comprise second transistors, wherein said second level is above said third level, wherein said second transistors are self-aligned to said first transistors, being processed following a same lithography step; and a fourth level comprising periphery circuits, said periphery circuits comprise connections by said second metal, wherein said periphery circuits are adapted to control said first memory cells and said second memory cells, and wherein said periphery circuits are atop said first memory cells and said second memory cells.
 9. The 3D semiconductor device according to claim 8, wherein at least one of said second transistors comprises a source, a channel, and a drain, and wherein said source, said channel, and said drain have a same dopant type.
 10. The 3D semiconductor device according to claim 8, wherein at least one of said second transistors comprises a polysilicon channel.
 11. The 3D semiconductor device according to claim 8, wherein said significantly greater current comprises at least 50% higher current carrying capacity of interconnect wire made by said second metal layer compared to current carrying capacity of interconnect wire made by said first metal layer or said third metal layer.
 12. The 3D semiconductor device according to claim 8, wherein at least one of said first transistors comprises a source, a channel, and a drain, and wherein said source, said channel, and said drain have a same dopant type.
 13. The 3D semiconductor device according to claim 8, wherein said first level is below said third level.
 14. The 3D semiconductor device according to claim 8, further comprising: connections to an external device, wherein said connections are above said fourth level and provide connections from said external device to said periphery circuits.
 15. A 3D semiconductor device, the device comprising; a first level comprising a single crystal layer, a first metal layer, a second metal layer above said first metal layer, and a third metal layer above said second metal layer, wherein said second metal layer is significantly thicker than either said third metal layer or said first metal layer; a second level comprising a first array of first memory cells, each of said first memory cells comprise first transistors; a third level comprising a second array of second memory cells, each of said second memory cells comprise second transistors, wherein said second level is above said third level, wherein said second transistors are self-aligned to said first transistors, being processed following a same lithography step; and periphery circuits connected by said second metal to control said first memory cells and said second memory cells, wherein said periphery circuits are either underneath said first memory cells and said second memory cells or atop said first memory cells and said second memory cells.
 16. The 3D semiconductor device according to claim 15, wherein at least one of said second transistors comprises a source, a channel, and a drain, and wherein said source, said channel, and said drain have a same dopant type.
 17. The 3D semiconductor device according to claim 15, wherein at least one of said second transistors comprises a polysilicon channel.
 18. The 3D semiconductor device according to claim 15, wherein said significantly thicker is at least 50% thicker.
 19. The 3D semiconductor device according to claim 15, wherein said periphery circuits are underneath said first memory cells and said second memory cells.
 20. The 3D semiconductor device according to claim 15, wherein said first memory cells and said second memory cells are non-volatile NAND memory type cells. 